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Abstract

Two discriminative techniques are described (and evaluated) for estimating the parameters of the Gaussians in a large vocabulary speech-recognition system. The first technique is based on using a modification of the MMI objective function, and appears to provide no improvement over standard ML estimation. The second technique is based on a heuristic correction of the Gaussian parameters, and is seen to give a 2-5% improvement over ML estimation. 2 INTRODUCTION One common feature of many speech-recognition systems is that they are based on statistical methods i.e., the acoustic observations are modelled by probability-density-functions (pdf's), whose parameters are estimated statistically, from large amounts of training data. Typically, maximum-likelihood (ML) estimation is used; i.e., given the correct lexical transcription of the training data, the objective of the estimation is to maximize the likelihood of the training observations (feature vectors), conditioned on the correct lex...